The material for manufacturing the bobbin body can be divided into two groups, the thermoplastic material and the thermosetting material. The thermoplastic material is a linear polymer which has a higher flexibility and a higher strength but has a poor heat resistance in comparison with the thermosetting material. The strength of the thermoplastic material is lowered as the ambient temperature is increased. The cost for increasing the heat resistance of the thermoplastic material is high and uneconomic.
The conventional bobbins 10, 20 are shown in FIG. 1 and FIG. 2. The whole bodies of bobbins 10, 20 are made of a thermoplastic or a thermosetting material by one time of injection molding. The thermoplastic material is the most popular material for producing a bobbin because it has a better mechanical property and a lower price. However, the thermoplastic material has a poor heat-resistance and there is a lot of heat conducting from the pins to the bobbin body when the soldered threads are held on the pins so that the bobbin body cracks and the pins fall off.
The thermosetting material has a higher heat resistance because of its network molecular structure. When the bobbin body is made of the thermosetting material, it can sustain the heat conducting from the pins. However, the strength of the thermosetting material is poor. The bobbin body made of the thermosetting material is very easily to crack when it rotates at high speed for reeling thereon threads.
The main purpose of the present invention is to produce a bobbin which can combine both of the advantages of the thermoplastic and thermosetting materials. The bobbin according to the present invention is economic and practical.